USDA Hardiness Zone 12a
Frost Dates for 96789 — Mililani, Hawaii
NOAA 1991–2020 normals from Upper Wahiawa 874.3, HI (1,006 ft), 3 miles north.
Updated
No night at or below 32°F was recorded at Upper Wahiawa 874.3, HI in 1991–2020, not even 36°F, so Mililani has no frost dates to plan around; the coolest month, February, averages a low of 60°F.
- Winters with a freeze
- 0%
- Winters with 36°F
- 0%
- Coldest month low
- 60°F
- Hardiness zone
- 12a
32°F or below, 1991–2020
frost possible on leaves
average, February
50 to 55°F (10.0 to 12.8°C) coldest night
- First snow
- Rare
- Last snow
- Rare
- Winters with snow
- 0%
- Snow per year
- 0"
median, 1991–2020
median, 1991–2020
0 of 20 observed
NOAA normal
Frost risk by date in Mililani
Upper Wahiawa 874.3, HI, 3 miles north of Mililani, did not record a night at or below 32°F in 1991–2020. 36 of the 37 other Hawaii stations behind this site's ZIP pages recorded no 32°F night either.
Freeze probabilities 1991–2020 at Upper Wahiawa 874.3, HI, from NOAA NCEI U.S. Climate Normals. Where a temperature is reached in fewer than 99.5% of years, the dates describe only the years that reach it. Not a forecast.
Frost risk on any date in 96789 →Compare Mililani with another place →
Weather by month in Mililani
August is the warmest month at Upper Wahiawa 874.3, HI, averaging 83°F by day and 68°F at night; February is the coldest at 76°F and 60°F. Not one month recorded a 32°F night; the lowest monthly average low is 60°F.
Warmth for growing adds up to 7,985 growing degree days a year (base 50°F), fewer than at 77% of the 35 Hawaii stations. 46% of them (3,657) have built up by the end of June, and August adds the most, 791. Precipitation totals 64.1 inches a year, most in December (7.5") and least in August (4.0"); May to September bring 35% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 76 | 61 | 5.2 | 0% | 0 | 572 |
| Feb | 76 | 60 | 4.3 | 0% | 0 | 503 |
| Mar | 77 | 62 | 6.3 | 0% | 0 | 597 |
| Apr | 77 | 63 | 5.6 | 0% | 0 | 606 |
| May | 79 | 65 | 4.3 | 0% | 0 | 677 |
| Jun | 80 | 67 | 4.2 | 0% | 0 | 702 |
| Jul | 82 | 67 | 5.2 | 0% | 0 | 756 |
| Aug | 83 | 68 | 4.0 | 0% | 0 | 791 |
| Sep | 83 | 67 | 4.6 | 0% | 0 | 753 |
| Oct | 82 | 66 | 5.8 | 0% | 0 | 743 |
| Nov | 79 | 65 | 7.1 | 0% | 0 | 665 |
| Dec | 77 | 63 | 7.5 | 0% | 0 | 622 |
Monthly normals 1991–2020 at Upper Wahiawa 874.3, HI (1,006 ft), NOAA NCEI. "32°F night": chance of at least one in the month. GDD: growing degree days, base 50°F.
Compared with the next station
The nearest other station, Poamoho Exp Fm 855.2, HI, 7 miles northwest of Mililani and 284 feet lower, has no 32°F night on record either, and a coolest-month low 2°F warmer (62°F).
When it snows in Mililani, Hawaii
Measurable snow is rare here: only 0 of 20 winters from 1991 to 2020 recorded 0.1 inch or more at Upper Wahiawa 874.3, HI, 2.8 miles away, so there is no typical first-snow date to plan around.
Where these figures come from
ZIP 96789 is 3 miles from Upper Wahiawa 874.3, HI, which stands at 1,006 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 1 other ZIP code shares the station. The 2023 USDA Plant Hardiness Zone Map lists ZIP 96789 in zone 12a, the band where the coldest night of the year averaged 50 to 55°F (10.0 to 12.8°C) over 1991–2020; a zone describes winter lows, not frost dates.
Hardiness zone and temperature range: USDA Plant Hardiness Zone Map 2023 (USDA-ARS, Oregon State University), ZIP-code listing, unchanged. °C converted from °F by this site.
Thirty-year averages, not a forecast: check the forecast before planting out. How stations are matched and which pages are offered to search engines: methodology.